Selective mtDNA mutation accumulation results in β-cell apoptosis and diabetes development

To test the hypothesis that somatic mitochondrial (mt)DNA mutation accumulation predisposes mice to β-cell loss and diabetes development, transgenic mice expressing a proofreading-deficient mtDNA polymerase-γ under the control of the rat insulin-1 promoter were generated. At 6 wk of age, mtDNA mutations reached 0.01% (1.05 mutations/10,000 bp) in islets isolated from transgenic mice. This mutational burden is associated with impaired glucose tolerance and a diabetes prevalence of 52% in male transgenic mice. Female transgenic mice maintain slightly elevated fasting glucose levels, mild glucose intolerance, and a diabetes prevalence of 14%. Diabetes in transgenic animals is associated with insulin insufficiency that results from a significant reduction in β-cell mass. Importantly, apoptosis of β-cells is increased 7-fold in female and 11-fold in male transgenic mice compared with littermate controls. These results are consistent with a causative role of somatic mtDNA mutation accumulation in the loss of β-cell mass and diabetes development.